Passive fire protection of structures and components is an area that is receiving increased attention. In this context the term “passive” means the use of materials that impart a barrier to fire and the results of fire such as intense heat. Passive fire protection systems are used extensively throughout the building and construction, mining and infrastructure, defense and transportation industries and typically function by counteracting the movement of heat and/or smoke, by sealing holes, by prolonging stability of structures to which the system is applied and/or by creating thermal and/or physical barriers to the passage of fire, heat and smoke.
Typically, in some passive fire protection applications, for example, gap filling for access spaces in a structure, gap-filling in wall penetrations for pipes and ducts, gap filling between panels, expansion joints, thermal insulation for ducts and pipes, door cores, seals in various applications, coatings on building panels, barrier coatings on various applications, there is a requirement for the material to exhibit minimal shrinkage and good strength at the high temperatures experienced in a fire. Foams have advantages over solid materials that in this case include lower densities for weight reduction, better acoustic and thermal insulation properties and greater flexibility.
When exposed to a fire (generally up to and exceeding about 1000° C.) polyurethane foams soften, collapse and finally pyrolyze leaving nothing or very little carbonaceous residue. Hence the polyurethane foam is unable to continue to fill the volume it occupied prior to exposure to fire making it incapable of functioning as an effective fire barrier. One way of making a fire barrier material of polyurethane base is to incorporate additives that can form and retain a solid residue of near identical shape and size with sufficient cohesiveness and strength at all stages on exposure to fire. Polyurethane foams must therefore contain inorganic components that confer the required fire barrier properties by providing a porous ceramic barrier to the passage of the fire.
Foams used in passive fire protection applications may be prepared by three approaches.
One approach involves impregnating a polyurethane foam structure with inorganic components that will generate a refractory residue on exposure to fire. British Patent 2251623 (Wexler et al.) describes a fire resistant sealing material prepared by impregnating foam, such as polyurethane foam, with a composition containing inorganic filler, sintering agent and optionally other additives. This approach is expensive as the process of infusion involves a separate operation and necessitates the subsequent removal of the aqueous carrier used in impregnation of the inorganic components. Foams prepared in this way can be wet, sticky and difficult to handle.
Another approach, described for example in U.S. Pat. Nos. 6,313,186 and 6,610,756, involves forming an inorganic foam containing a physically integrated polyurethane. These materials tend to have high density, low compressibility and inherent brittleness.
Another approach involves making the polyurethane foam in the presence of inorganic compounds that react to provide a ceramic foam with the required properties upon exposure to fire. Our International Patent Publication WO 2004/035711 describes such an approach in which the fire resistant polymer composition contains at least 15% by weight based on the total weight of the composition of a polymer base composition comprising at least 50% by weight of an organic polymer; at least 15% by weight based on the total weight of the composition of a silicate mineral filler; and at least one source of fluxing oxide, wherein after exposure to an elevated temperature experienced under fire conditions, the fluxing oxide is present in an amount of from 1 to 15% by weight of the residue.
In the case of low density polyurethane foams the desirability for fire barrier properties to be maintained under fire conditions has been extremely difficult to meet. Intumescent foams have been used that expand under fire conditions but any further loss of density generally results in disintegration of the product under fire condition or the formation of a residue of such poor strength as to provide no significant barrier to the passage of fire.
The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of this application.